i.e. an analytic function of \(\mathcal {Z}\)  or \(\mathcal {Z}^{\star }\) , depending on which side of the interface we are considering. This mode is a special case of the one–way propagation Jackiw–Rebbi mode of the two dimensional Dirac equation [1]}. Again, the idea of enforcing one–way propagation of a wave through demanding analyticity—in this case finding unidirectional interface state through connecting materials where the wave behaves as a function of \(\mathcal {Z}\)  and \(\mathcal {Z}^{\star }\) —is a simple shortcut to findings that are ordinarily connected with topological arguments [2]}.
